Re: [PATCH v4 2/3] iio: adc: Support ROHM BD79112 ADC/GPIO

[Matti Vaittinen <mazziesaccount@gmail.com>]

Morning Jonathan,

On 10/09/2025 20:46, Jonathan Cameron wrote:
> On Wed, 10 Sep 2025 14:24:35 +0300
> Matti Vaittinen <mazziesaccount@gmail.com> wrote:
> 
>> The ROHM BD79112 is an ADC/GPIO with 32 channels. The channel inputs can
>> be used as ADC or GPIO. Using the GPIOs as IRQ sources isn't supported.
>>
>> The ADC is 12-bit, supporting input voltages up to 5.7V, and separate I/O
>> voltage supply. Maximum SPI clock rate is 20 MHz (10 MHz with
>> daisy-chain configuration) and maximum sampling rate is 1MSPS.
>>
>> The IC does also support CRC but it is not implemented in the driver.
>>
>> Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
> 
> Hi Matti,
> 
> A few trivial things that I'll tidy up if nothing else comes up (I might not
> bother given how trivial they are!)

Thanks again!

> Also one question. I couldn't immediately follow why any random register
> read is sanity checking if an ADC pin is configured as GPIO.
> 

Ah. Valid question! I see my comment below is partially wrong.


>> +/*
>> + * Read transaction consists of two 16-bit sequences separated by CSB.
>> + * For register read, 'IOSET' bit must be set. For ADC read, IOSET is cleared
>> + * and ADDR equals the channel number (0 ... 31).
>> + *
>> + * First 16-bit sequence, MOSI as below, MISO data ignored:
>> + * - SCK: | 1 | 2 |   3   |    4   | 5 .. 8 | 9 .. 16 |
>> + * - MOSI:| 0 | 0 | IOSET | RW (1) |  ADDR  |  8'b0   |
>> + *
>> + * CSB released and re-acquired between these sequences
>> + *
>> + * Second 16-bit sequence, MISO as below, MOSI data ignored:
>> + *   For Register read data is 8 bits:
>> + *   - SCK: | 1 .. 8 |   9 .. 16   |
>> + *   - MISO:|  8'b0  | 8-bit data  |
>> + *
>> + *   For ADC read data is 12 bits:
>> + *   - SCK: | 1 .. 4 |   4 .. 16   |
>> + *   - MISO:|  4'b0  | 12-bit data |

This is not 100% true. I overlooked the ADC read "status flag" when 
adding this comment for the ADC data reading.

This should be:

  *   For ADC, read data is 12 bits prepended with a status flag:
  *   - SCK: | 1 |      2      | 3  4 |   4 .. 16   |
  *   - MISO:| 0 | STATUS_FLAG | 2'b0 | 12-bit data |

The 'STATUS_FLAG' is set if the input pin is configured as a GPIO.

>> + */
>> +static int bd79112_reg_read(void *context, unsigned int reg, unsigned int *val)
>> +{
>> +	struct bd79112_data *data = context;
>> +	int ret;
>> +
>> +	if (reg & BD79112_BIT_IO)
>> +		reg |= BD79112_BIT_RW;
>> +
>> +	data->read_tx[0] = reg;
>> +
>> +	ret = spi_sync(data->spi, &data->read_msg);
>> +	if (!ret)
>> +		*val = be16_to_cpu(data->read_rx);
>> +
>> +	if (reg & BD79112_BIT_IO && *val & BD79112_ADC_STATUS_FLAG)
>> +		dev_err(data->dev, "ADC pin configured as GPIO\n");
> 
> Why are we checking this in a regmap callback?
> Maybe it needs rewording and the point is some missmatch in what we
> can read vs the state?
> 
>> +
>> +	return ret;
>> +}
> 
>> +
>> +static int bd79112_probe(struct spi_device *spi)
>> +{
>> +	struct bd79112_data *data;
>> +	struct iio_dev *iio_dev;
>> +	struct iio_chan_spec *cs;
>> +	struct device *dev = &spi->dev;
>> +	unsigned long gpio_pins, pin;
>> +	unsigned int i;
>> +	int ret;
>> +
>> +	iio_dev = devm_iio_device_alloc(dev, sizeof(*data));
>> +	if (!iio_dev)
>> +		return -ENOMEM;
>> +
>> +	data = iio_priv(iio_dev);
>> +	data->spi = spi;
>> +	data->dev = dev;
>> +	data->map = devm_regmap_init(&spi->dev, NULL, data, &bd79112_regmap);
> 
> 	data->mpa = devm_regmap_init(dev, ...
> 
> 
>> +	if (IS_ERR(data->map))
>> +		return dev_err_probe(dev, PTR_ERR(data->map),
>> +				     "Failed to initialize Regmap\n");
>> +
>> +	ret = devm_regulator_get_enable_read_voltage(dev, "vdd");
>> +	if (ret < 0)
>> +		return dev_err_probe(dev, ret, "Failed to get the Vdd\n");
>> +
>> +	data->vref_mv = ret / 1000;
>> +
>> +	ret = devm_regulator_get_enable(dev, "iovdd");
>> +	if (ret < 0)
>> +		return dev_err_probe(dev, ret, "Failed to enable I/O voltage\n");
>> +
>> +	data->read_xfer[0].tx_buf = &data->read_tx[0];
>> +	data->read_xfer[0].len = sizeof(data->read_tx);
>> +	data->read_xfer[0].cs_change = 1;
>> +	data->read_xfer[1].rx_buf = &data->read_rx;
>> +	data->read_xfer[1].len = sizeof(data->read_rx);
>> +	spi_message_init_with_transfers(&data->read_msg, data->read_xfer, 2);
>> +
>> +	data->write_xfer.tx_buf = &data->reg_write_tx[0];
>> +	data->write_xfer.len = sizeof(data->reg_write_tx);
>> +	spi_message_init_with_transfers(&data->write_msg, &data->write_xfer, 1);
>> +
>> +	ret = devm_iio_adc_device_alloc_chaninfo_se(dev, &bd79112_chan_template,
>> +						    BD79112_MAX_NUM_CHANNELS - 1,
>> +						    &cs);
>> +
>> +	/* Register all pins as GPIOs if there are no ADC channels */
>> +	if (ret == -ENOENT)
>> +		goto register_gpios;
>> +
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	iio_dev->num_channels = ret;
>> +	iio_dev->channels = cs;
>> +
>> +	for (i = 0; i < iio_dev->num_channels; i++) {
>> +		unsigned int ch = cs[i].channel;
>> +
>> +		cs[i].datasheet_name = bd79112_chan_names[ch];
> 
> Could have done
> 
> 		cs[i].datasheet_name = bd79112_chan_names[cs[i].channel];
> 
> and I don't think it makes it harder to read, but doesn't matter enough to respin.

I kind of agree. It stays short and allows us to get rid of the 
brackets. Thanks!

I can still re-spin this later this week, assuming you rather not fix 
the data-format comment while applying :)

Thanks for pointing this out!

Yours,
	-- Matti